In many modern wireless communication applications, such as cellular networks (and particularly advanced cellular standards, such as LTE), the required traffic capacities in the uplink and downlink directions are not identical. For example, Internet browsing typically requires much higher traffic capacity on the downlink than on the uplink. (In the context of the present patent application and in the claims, the term “traffic capacity” refers to the amount of information that is conveyed over a communication link per unit time.) It has been estimated that the overall downlink traffic demand in wireless networks is between three and ten times larger than the corresponding uplink demand. In commercial wireless networks that use frequency-domain duplexing (FDD), however, the available frequency spectrum is usually partitioned in a fixed manner (typically equal) between downlink and uplink.
Because of the mismatch between traffic demand and frequency allocation, wireless networks fail to make full use of the available traffic capacity of both the uplink and the downlink simultaneously, and are therefore limited by the capacity of one of the link directions. As a result, FDD networks make sub-optimal use of their available transmission spectrum. Furthermore, even if the frequency spectrum were to be divided unequally between uplink and downlink, to achieve a better match to the traffic demand, some inefficiency would still remain, as traffic loads in the uplink and downlink directions may change over time.